1. Field
The present disclosure relates to the field of communications, and in particular to a signal transmission apparatus and multicarrier communication system.
2. Description of the Related Art
A multicarrier communication system is a communication system based on multicarrier modulation, which is widely used in wireless and access networks at present due to its advantages, such as high transmission rate, high spectral efficiency, and multipath and frequency domain fading proof, and to which wide attention is paid and studied as being taken as an important solution for future higher speed and complex network communications.
A channel signal to noise ratio (SNR) probing technique is a necessary technique important to the multicarrier communication system. FIG. 1 is a schematic diagram of a channel probing stage in the multicarrier communication system. As shown in FIG. 1, its main function is that before actual transmission, channel information is collected by using a probe signal, so as to estimate signal to noise ratios of subcarriers of a channel at the actual transmission stage; then modulation formats and power allocation adopted at the actual transmission stage are selected for available subcarriers in an adaptive optimization or direct designation manner according to recommended actual transmission signal configuration selected according to the signal to noise ratios, such as abandoning channel subcarriers of bad conditions, so as to improve a transmission rate or performance. It can be seen that before actual transmission, obtaining a signal to noise ratio consistent with that in the actual transmission by using the probe signal is key to success of the transmission. This is because that first, optimal transmission configuration can be obtained and transmission efficiency can be maximized only when a correct channel signal to noise ratio in the actual transmission is obtained; and second, the transmission performance can be accurately estimated and services can be provided to design of the system only when the signal to noise ratio in the actual transmission is correctly obtained before the actual transmission, such as avoiding invalid transmission unsatisfying traffic demands, etc.
Currently, methods for probing a channel signal to noise ratio of each subcarrier are relatively simple and direct. FIG. 2 is a schematic diagram of a method for probing a channel signal to noise ratio of each subcarrier in the relevant art. As shown in FIG. 2, a predefined probe signal is generated at and transmitted from a transmitting end, and the signal to noise ratio of each subcarrier is obtained by comparing an original probe signal with the predefined probe signal after it is subjected to channel transmission and receiving end processing; then, based on an important assumption that a signal to noise ratio of a probe signal may feature a signal to noise ratio of an actually transmitted signal, the signal to noise ratio of each subcarrier at the actual transmission stage is directly obtained. For example, IEEE 802.16e is a standard provided by the IEEE for wideband wireless metropolitan area network communications, in which an adaptive modulation technique of the applied scalable orthogonal frequency division multiple access determines channel modulation under different channel conditions based on such a method for probing a channel signal to noise ratio.
Documents advantageous to the understanding of the present disclosure and conventional technologies are listed below, and are incorporated herein by reference, as they are fully described in this text.    Reference 1: John A. C. Bingham, ADSL, VDSL, and Multicarrier Modulation, 5th chapter, 2000; and    Reference 2: IEEE P802.16e, IEEE standard for local and metropolitan area networks, 2005.
It should be noted that the above description of the background art is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background art of the present disclosure.